In the deployment, operation and administration of communication networks, knowledge of network performance at specific locations and for specific communication resources (such as frequencies, carriers, etc.) is vital.
For obtaining such required knowledge of network performance, drive tests are typically to be performed by the network operator. Yet, performing such manual drive tests is expensive and cumbersome. Accordingly, efforts for minimizing drive tests (MDT) are made in current standardization work, e.g. by 3GPP (Third Generation Partnership Project). In the MDT context, automatic data collection of UE (user equipment) measurements (and automatic UE measurements) are defined to enable easier monitoring of network performance and, consequently, to replace or at least reduce the need for expensive manual drive tests.
Currently, two MDT approaches (for MDT measurement, logging and reporting) are agreed and accepted in 3GPP. The one approach is referred to as Immediate MDT reporting and the other approach is referred to as Logged MDT reporting. In Immediate MDT reporting, MDT configuration as well as MDT data collection are done when the relevant UE is in connected mode. In Logged MDT reporting, MDT configuration is done when the relevant UE is in connected mode, and MDT data collection is done when the relevant UE is in idle mode.
The measurement, and reporting functions follows general rules according to current specifications, such as defined e.g. in 3GPP TS 36.133. According to such general rules, besides certain freedom in specific cases, the UE is at least in certain cases mandated to perform serving cell measurements only.
Therefore, following the current general rules, is problematic in scenarios in which terminal such as a UE may be served by more than one cell, i.e. the terminal has allocated more than a single communication resource for being served by the network. This may specifically the case in carrier aggregation (CA).
In carrier aggregation (CA), two or more carriers, typically referred to as component carriers (CCs), are aggregated for a terminal in order to support wider transmission bandwidths (e.g. up to 100 MHz). In such CA scenario, a terminal may have a primary carrier representing the serving cell as well as a set of cells represented by a primary cell and one or more aggregated secondary carriers (e.g. for supporting wider transmission bandwidth) representing alternative cells for being chosen as a new serving cell.
Following the current general rules for MDT reporting, in a CA scenario, the UE only measures the primary carrier being regarded as the serving cell (in particular, when it is in idle mode). Only under specific cases, the UE may measure a secondary carrier (instead of the primary carrier). Namely, the UE only measures all indicated inter-frequency/RAT (radio access technology) and intrafrequency neighbors in case the serving cell signal becomes weak in order to choose a new serving cell. Accordingly, the UE typically only measures the carrier currently/prospectively representing the serving cell, which only depends on signal strength characteristics being subject to dynamic and uncontrollable changes. Stated in other words, in CA scenarios, (logged/immediate) MDT reporting mainly depends on which carrier the (idle/connected) UE currently camps on, instead of a network-controllable configuration. Furthermore, in CA scenarios, different UEs have different primary carriers, thus different UEs camping on different carriers (e.g. after going to idle mode), which may lead to unequal measurement quantities on different carriers, instead of a network-controllable configuration.
Moreover, in CA scenarios, it is likely that resources may expand across multiple carriers. Since different carriers may have different coverage, it would be beneficial to collect information about radio conditions and discover differences between the individual carriers. Also for carriers having the same coverage, it would be beneficial to be able to compare measurement results and figure out optimum configuration settings. However, with the current general rules for MDT reporting, only the measurement, and reporting of the serving cell may be ensured.
From the MDT point of view, it would be better to know the performance of all of the CA carriers (i.e. the primary carrier and the secondary carrier/s) at the same location and time when CA is deployed. In view thereof, automatic data collection of UE measurements (and automatic UE measurements) are required, the configuration of which is controllable from the network side.
In view of the above, there is a need for mechanisms enabling a network-controlled configuration of terminal measurements in carrier aggregation. Specifically, there is a need for mechanisms enabling the determination of one or more specific carriers (primary and/or secondary carriers) for which MDT reporting is desired and/or enabling equal measurement results/quantities for different carriers (primary and/or secondary carriers) in MDT reporting.
Accordingly, there is a demand for mechanisms for terminal measurement configuration in carrier aggregation.